Indication of user equipment transmit power capacity in carrier aggregation

ABSTRACT

A method of power headroom reporting (PHR) is proposed. A UE is configured with a plurality of component carriers (CCs) and is served by one or more power amplifiers (PAs) in a wireless system with carrier aggregation. The UE determines transmit power limitation (TPL) information that comprises a set of TPL values, each TPL value corresponds to a UE-configured maximum transmit power for UE-level, PA-level, and CC-level. The TPL information is then reduced to non-redundant TPL values. Based on the non-redundant TPL values, the UE determines power headroom (PH) information that comprises a set of PH values. Each PH value equals to a TPL value subtracted by a UE-calculated transmit power. The UE reports the PH information to a base station via a fixed-length or variable-length MAC CE at each PHR reporting instance.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation, and claims priority under 35 U.S.C.§120 from nonprovisional U.S. patent application Ser. No. 13/200,783,entitled “Method of Uplink MDT Measurement,” filed on Sep. 29, 2011, thesubject matter of which is incorporated herein by reference. applicationSer. No. 13/200,783 was issued on May 20, 2014 as U.S. Pat. No.8,730,829. Application Ser. No. 13/200,783, in turn, claims priorityunder 35 U.S.C. §119 from U.S. Provisional Application No. 61/388,672,entitled “Reporting Mechanism for Transmission Power in CarrierAggregation,” filed on Oct. 1, 2010; U.S. Provisional Application No.61/411,062, entitled “Mechanism for Reporting Maximum Transmission Powerin Carrier Aggregation,” filed on Nov. 8, 2010; U.S. ProvisionalApplication No. 61/481,702, entitled “Indication of User EquipmentTransmit Power Capacity in Carrier Aggregation,” filed on May 2, 2011,the subject matter of which is incorporated herein by reference.

TECHNICAL FIELD

The disclosed embodiments relate generally to wireless networkcommunications, and, more particularly, to configuring and reportingmaximum transmission power and power headroom from user equipments tobase stations in carrier aggregation systems.

BACKGROUND

A Long-Term Evolution (LTE) system offers high peak data rates, lowlatency, improved system capacity, and low operating cost resulting fromsimple network architecture. An LTE system also provides seamlessintegration to older wireless network, such as GSM, CDMA and UniversalMobile Telecommunication System (UMTS). Enhancements to LTE systems areconsidered so that they can meet or exceed International MobileTelecommunications Advanced (IMT-Advanced) fourth generation (4G)standard. One of the key enhancements is to support bandwidth up to 100MHz and be backwards compatible with the existing wireless networksystem. Carrier aggregation (CA) is introduced to improve systemthroughput. With carrier aggregation, the LTE-Advanced system cansupport peak target data rates in excess of 1 Gbps in the downlink (DL)and 500 Mbps in the uplink (UL). Such technology is attractive becauseit allows operators to aggregate several smaller contiguous ornon-continuous component carriers (CC) to provide a larger systembandwidth, and provides backward compatibility by allowing legacy usersto access the system by using one of the component carriers.

Orthogonal frequency division multiplexing (OFDM) radio technology hasbeen incorporated into LTE/LTE-A because it enables high data bandwidthto be transmitted efficiently while still providing a high degree ofresilience to reflections and interference. In OFDM communicationsystems, the transmit power of each mobile station (UE) needs to bemaintained at a certain level and regulated by the network. The maximumtransmit power of each UE, however, is different depending on UEcapacity. Power headroom report (PHR) is a mechanism to configure the UEto provide its power capacity and usage to the network. A UE uses PHRmechanism to periodically provide its serving base station (eNB) withits power headroom (PH), which is defined as a power offset between aUE-configured maximum transmit power and a UE-calculated current UEtransmit power. Based on the received PH information, the eNB canregulate the UE transmit power with proper resource allocation.

FIG. 1 (Prior Art) illustrates a power headroom (PH) and other relatedparameters of a UE in LTE Rel-8/9 systems without carrier aggregation.The PH value of the UE is defined in Eq. (1), while the UE-configuredmaximum output power P_(CMAX) is defined in Eq. (2):PH=P _(CMAX) −UE transmit Power  (1)P _(CMAX) _(_) _(L) <=P _(CMAX) <=P _(CMAX) _(_) _(H)  (2)where

-   -   P_(CMAX) _(_) _(L)=MIN {P_(EMAX)−ΔT_(C),        P_(POWERCLASS)-MPR-A-MPR-ΔT_(C)}    -   P_(CMAC) _(_) _(H)=MIN {P_(EMAX), P_(POWERCLASS)}    -   P_(EMAX) is configured by higher layers    -   P_(POWERCLASS) is the maximum UE output power    -   Maximum Power Reduction (MPR): the maximum allowed reduction of        maximum power of certain modulation order and the number of        resource blocks    -   Additional Maximum Power Reduction (A-MPR): the maximum allowed        reduction of maximum power for the number of resource blocks and        the band    -   ΔT_(C)=1.5 dB when the CC at the edge of a band; 0 dB otherwise

FIG. 2 (Prior Art) illustrates multiple power headroom values and otherrelated parameters of a UE in LTE Rel-10 systems with carrieraggregation. In LTE Rel-10 systems, more flexible resource assignmentsare required to support advanced features including carrier aggregation,simultaneous PUCCH (Physical Uplink Control Channel) and PUSCH (PhysicalUplink Shared Channel) transmission, parallel transmission of PUSCHs onmultiple CCs, multi-clustered PUSCH, and power scaling. In the exampleof FIG. 2, the UE is configured with two component carriers CC1 and CC2.The UE-configured maximum output powers for CC1 (e.g., P_(CMAX,C1)) andfor CC2 (e.g., P_(CMAX,C2)) depend on upper layer configurations (e.g.,P_(MAX) _(_) _(CC1) and P_(MAX) _(_) _(CC1)) and other CC-relatedparameters such as MPR, A-MPR, and ΔT_(C). Furthermore, because CC1 andCC2 belong to the same UE, and are served by the same or different poweramplifier(s), the total maximum output power of both CC1 and CC2 may belimited to additional constraints such as P_(MAX) _(_) _(UE) or P_(MAX)_(_) _(PA). As a result, multiple PH values need to be reported to theeNB for UE transmit power control. Therefore, the existing PHR mechanismfor Rel-8/9 systems without CA is no longer adequate to consider varioustransmit power limitations imposed on multiple configured CCs of a UE,on power amplifiers that serve the CCs, and on the UE.

SUMMARY

A method of power headroom reporting (PHR) is proposed. A UE isconfigured with a plurality of component carriers (CCs) and is served byone or more power amplifiers (PAs) in a wireless system with carrieraggregation. The UE determines transmit power limitation (TPL)information that comprises a set of TPL values, each TPL valuecorresponds to a UE-configured maximum transmit power for UE-level,PA-level, and CC-level. The TPL information is then reduced tonon-redundant TPL values. Based on the non-redundant TPL values, the UEdetermines power headroom (PH) information that comprises a set of PHvalues. Each PH value equals to a TPL value subtracted by aUE-calculated transmit power.

A new PHR format is proposed for multi-layer power headroom reporting.In one example, the UE reports the PH information to a base station viaa fixed-length MAC CE at each PHR reporting instance. In anotherexample, the UE reports the PH information to a base station via avariable-length MAC CE at each PHR reporting instance. The lengthindication may be included in the MAC sub-header or in the MAC PDU. Anew LCID is assigned in the MAC sub-header for MAC CE PHR.

Other embodiments and advantages are described in the detaileddescription below. This summary does not purport to define theinvention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, where like numerals indicate like components,illustrate embodiments of the invention.

FIG. 1 (Prior Art) illustrates a power headroom and other relatedparameters of a UE in LTE Rel-8/9 systems without carrier aggregation.

FIG. 2 (Prior Art) illustrates multiple power headroom values and otherrelated parameters of a UE in LTE Rel-10 systems with carrieraggregation.

FIG. 3 is a simplified block diagram of a user equipment and a basestation in an LTE/LTE-A Rel-10 wireless communication system with PHRmechanism in accordance with one novel aspect.

FIG. 4A illustrates a first example of TPL reduction when there is onlyone PA in a UE.

FIG. 4B illustrates a second example of TPL reduction when there is a PAserves only one CC.

FIG. 5 is a flow chart of a method of complete power headroom reporting.

FIGS. 6A and 6B are flow charts of a method of efficient power headroomreporting.

FIG. 7 illustrates a method of indicating UE transmit power capacity inaccordance with one novel aspect.

FIG. 8 is a flow chart of the method of indicating UE transmit powercapacity in accordance with one novel aspect.

FIG. 9 illustrates a PHR procedure between an eNB and a UE in accordancewith one novel aspect.

FIG. 10 illustrates examples of fixed-length MAC CE for power headroomreporting.

FIG. 11 illustrates examples of variable-length MAC CE for powerheadroom reporting.

FIG. 12 illustrates an embodiment of a new format for per UE PHR.

DETAILED DESCRIPTION

Reference will now be made in detail to some embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings.

FIG. 3 is a simplified block diagram of a user equipment UE301 and abase station eNB321 in an LTE/LTE-A Rel-10 wireless communication system300 in accordance with one novel aspect. In wireless communicationsystem 300, the transmit power of UE301 needs to be maintained at acertain level achieve desired channel quality and to maximize systemcapacity. Meanwhile, the transmit power of UE301 is regulated by eNB321so that coexisting systems are not severely interfered with each other.The allowable maximum transmit power, however, is different for each UEdepending on the capacity of the UE. For example, for a UE with verygood capability on the suppression of out-of-band emission and spuriousemission, its transmission power is allowed to be larger than a UE witha worse emission suppression capability. In addition, the maximumtransmit power of a UE is related to resource allocation of the UE(e.g., the modulation and coding scheme (MCS) and the resourcelocation/size occupied by the UE). Power headroom report (PHR) is amechanism that configures a UE to report its power capacity and usage.

In the example of FIG. 3, UE301 comprises memory 302, a processor 303, apower control module 304, and a transmitter and receiver 305 coupled toantenna 306. Similarly, eNB321 comprises memory 322, a processor 323, apower control module 324, and a transmitter and receiver 325 coupled toantenna 326. In LTE/LTE-A Rel-10 system 300 with carrier aggregation(CA), UE301 is configured with multiple component carriers (CCs), andeach carrier is served by a corresponding power amplifier (PA). In onenovel aspect, to facilitate the PHR mechanism, the transmit powerlimitations (TPL) of a UE is configured in three levels, a firstUE-level TPL, a second PA-level TPL, and a third CC-level TPL. Thedifferent levels of TPL information are then reduced to non-redundantTPL values for efficient power headroom reporting.

First, the CC-level TPL is to used to limit the transmit power of thei-th CC not be larger than P_(EMAX,i). P_(EMAX,i) is the maximumtransmit power for the i-th CC configured by higher layers. If theUE-configured maximum transmit power of the i-th CC is denoted asP_(MAX) _(_) _(CC,i) and the per-CC PH of the i-th CC is denoted asPH_(CC,i), then mathematically we have:PH_(CC,i) =P _(MAX) _(_) _(CC,i) −P _(CC,i)  (3)P _(EMAX,i) −ΔT _(C) <=P _(MAX) _(CC,i) <=P _(EMAX,i)  (4)where

-   -   ΔT_(C)=1.5 dB when the i-th CC is at the edge of a band; 0 dB        otherwise    -   P_(CC,i) is the transmit power of the i-th CC.

Second, the PA-level TPL is used to limit the output power of the j-thPA not be larger than P_(MAX) _(_) _(PA,j) to avoid bad efficiency andlarge out-of-band emission for the j-th PA. If the per-PA PH of the j-thPA is denoted as PH_(PA,j), then mathematically we have:PH_(PA,j) =P _(MAX) _(_) _(PA) −P _(PA,j)  (5)P _(POWERCLASS)−MPR_(PA,j) −A-MPR_(PA,j) −ΔT _(C) <=P _(MAX) _(_)_(PA,j) <=P _(POWERCLASS)  (6)where

-   -   P_(POWERCLASS) is the maximum UE output power    -   MPR_(PA,j): MPR for the resources of CCs served by the j-th PA,        and Maximum Power Reduction (MPR) is the maximum allowed        reduction of maximum power of certain modulation order and the        number of resource blocks    -   A-MPR_(PA,j): A-MPR for the resource of the CCs served by the        j-th PA, and Additional Maximum Power Reduction (A-MPR) is the        maximum allowed reduction of maximum power for the number of        resource blocks and the band    -   ΔT_(C) is the maximum of ΔT_(C,i)'s    -   P_(PA,j) is the sum of transmit powers of CCs served by the j-th        PA.

Third, the UE-level TPL is used to limit the total UE transmit power notbe larger than P_(POWERCLASS), which is the maximum UE output power. Ifthe UE-configured maximum transmit power of the UE is denoted as P_(MAX)_(_) _(UE), and the per-UE PH is denoted as PH_(UE), then mathematicallywe have:PH_(UE) =P _(MAX) _(_) _(UE) −P _(UE)  (7)P _(POWERCLASS) −ΔT _(C) <=P _(MAX) _(_) _(UE) <=P _(POWERCLASS)  (8)where

-   -   ΔT_(C)=0 dB or 1.5 dB    -   P_(UE) is the sum of transmit powers of all configured CCs in        the UE.

The UE-level, PA-level, and CC-level TPL information described aboveform a layered structure. The UE-level is the highest layer (l=1), thePA-level is the middle layer (l=2) and the CC-level is the lowest layer(l=3). The layered structure is represented by certain mapping ofsymbols. In one example, ((CC1, CC2), (CC3), (CC4, CC5)) represents thatthe UE has three PAs (PA1, PA2, and PA3), and that CC1 and CC2 sharePA1, CC3 uses PA2, and CC4 and CC5 share PA3. In another example,((CC1)) represents that there is only one PA in the UE and CC1 is servedby PA1. By considering the layered structure, the TPL information can bereduced accordingly when some of the TPL values in difference layers areredundant. In general, TPL values at layer-1 and layer-(l+1) can becombined into one TPL value, if the layer-(l+1) entity is the onlyentity inside the layer-1 entity.

FIGS. 4A and 4B illustrate examples of TPL reduction at different levelsin accordance with one novel aspect. In the example of FIG. 4A, UE401 isconfigured with three component carriers CC1, CC2, and CC3. All threeCCs are served by the same power amplifier PA1. Such layered structureis represented as ((CC1, CC2, CC3)). Without TPL reduction, differentTPL constraints in different levels are:CC1: P _(CC,1) <=P _(MAX) _(_) _(CC,1)  (A1)CC2: P _(CC,2) <=P _(MAX) _(_) _(CC,2)  (A2)CC3: P _(CC,3) <=P _(MAX) _(_) _(CC,3)  (A3)PA1: P _(CC,1) +P _(CC,2) +P _(CC,3) <=P _(MAX) _(_) _(PA,1)  (A4)UE: P _(CC,1) +P _(CC,2) +P _(CC,3) <=P _(MAX) _(_) _(UE)  (A5)

It can be seen from the above equations, that equation (A4) and equation(A5) may be reduced to one equation to represent one PA-level TPL, aslong as the right TPL constraint can be determined. Generally, if thereis only one PA (e.g., PA1) in a UE, and there are n active CCs (e.g.,CC1 to CCn), then the UE-level TPL can be replaced by the PA-level TPL.In order to replace the UE-level TPL (e.g., P_(MAX) _(_) _(UE)) by thePA-level TPL (e.g., P_(MAX) _(_) _(PA,1)), a new TPL (e.g., P_(MAX) _(_)_(UE,PA,1) _(_) _(UE)) is defined and its lower bound and upper boundare determined. Mathematically, we have the PA-level TPL and theUE-level TPL and their lower bound and upper bound are as follows:P _(CC1) +P _(CC2) + . . . +P _(CCn) <=P _(MAX) _(_) _(PA,1)  (A6)P _(CC1) +P _(CC2) + . . . +P _(CCn) <=P _(MAX) _(_) _(UE)  (A7)P _(POWERCLASS)−MPR_(PA,1) −A-MPR_(PA,1) −ΔT _(C) <=P _(MAX) _(_)_(PA,1) <=P _(POWERCLASS)  (A8)P _(POWERCLASS) −ΔT _(C) <=P _(MAX) _(_) _(UE) <=P _(POWERCLASS)  (A9)By combining (A6) and (A7) and combining (A8) and (A9), the new TPLP_(MAX) _(_) _(PA,1) _(_) _(UE) is defined as:P _(CC1) +P _(CC2) + . . . +P _(CCn) <=P _(MAX) _(_) _(PA,1) _(_)_(UE)  (A10)P _(POWERCLASS)−MPR_(PA,1) −A-MPR_(PA,1) −ΔT _(C) <=P _(MAX) _(_)_(PA,1) _(_) _(UE) <=P _(POWERCLASS)  (A11)

Because the upper bound of P_(MAX) _(_) _(PA,1) and P_(MAX) _(_) _(UE)are the same, the upper bound of P_(MAX) _(_) _(PA,1) _(_) _(UE)therefore is also P_(POWERCLASS). On the other hand, the lower bound ofP_(MAX) _(_) _(UE) is P_(POWERCLASS)−ΔT_(C), which represents thecapability of the duplex filter, while the lower bound of P_(MAX) _(_)_(PA,1) is P_(POWERCLASS)−MPR_(PA,1)−A-MPR_(PA,1)−ΔT_(C), whichrepresents the capability of the duplex filter and PA1. Therefore, thelower bound of P_(MAX) _(_) _(PA,1) _(_) _(UE) should be the same as thelower bound of P_(MAX) _(_) _(PA,1). Finally, it can be concluded thatP_(MAX) _(_) _(PA,1) _(_) _(UE):=P_(MAX) _(_) _(PA,1) and (A7) can beregarded as redundant.

In the example of FIG. 4B, UE402 is configured with three componentcarriers CC1, CC2, and CC3. CC1 and CC2 are served by a first poweramplifier PA1, while CC3 is served by a second power amplifier PA2. Suchlayered structure is represented as ((CC1, CC2), CC3)). Without TPLreduction, different TPL constraints in different levels are:CC1: P _(CC,1) <=P _(MAX) _(_) _(CC,1)  (B1)CC2: P _(CC,2) <=P _(MAX) _(_) _(CC,2)  (B2)CC3: P _(CC,3) <=P _(MAX) _(_) _(CC,3)  (B3)PA1: P _(CC,1) +P _(CC,2) <=P _(MAX) _(_) _(PA,1)  (B4)PA2: P _(CC,3) <=P _(MAX) _(_) _(PA,2)  (B5)UE: P _(CC,1) +P _(CC,2) +P _(CC,3) <=P _(MAX) _(_) _(UE)  (B6)

It can be seen from the above equations, that equation (B3) and equation(B5) may be reduced to one equation to represent one CC-level TPL, aslong as the right TPL constraint can be determined. Generally, if thej-th PA serves only the i-th CC, then the PA-level TPL can be replacedby the CC-level TPL. In order to replace the PA-level TPL (e.g., P_(MAX)_(_) _(PA,j)) by the CC-level TPL (e.g., P_(MAX) _(_) _(CC,i)) a new TPL(e.g., P_(MAX) _(_) _(PA,j) _(_) _(CC,i)) is defined and its lower boundand upper bound are determined. We have the CC-level TPL and thePA-level TPL and their lower bound and upper bound as follows:P _(CC,) <=P _(MAX) _(_) _(CC,i)  (B7)P _(CC,i) <=P _(MAX) _(_) _(PA,j)  (B8)P _(EMAX,i) −ΔT _(C,i) <=P _(MAX) _(_) _(CC,i) <=P _(EMAX,I)  (B9)P _(POWERCLASS)−MPR_(PA,j) −A-MPR_(PA,j) −ΔT _(C,i) <=P _(MAX) _(_)_(PA,j) <=P _(POWERCLASS)  (B10)

By combining (B7) and (B8) and combining (B9) and (B10), the new TPLP_(MAX) _(_) _(PA,j) _(_) _(CC,i) is defined as:P _(CC,i) <=P _(MAX) _(_) _(PA,j) _(_) _(CC,i)  (B11)min (P _(EMAX,I) −ΔT _(C) ,P _(POWERCLASS)−MPR_(PA,j) −A-MPR_(PA,j) −ΔT_(C,i))<=P _(MAX) _(_) _(PA,j) _(_) _(CC,I)<=min (P _(EMAX,i) ,P_(POWERCLASS))  (B12)

For upper bound, the upper bound of P_(MAX) _(_) _(PA,j) _(_) _(CC,i) isclearly min (P_(EMAX,i), P_(POWERCLASS)) On the other hand, the lowerbound of P_(MAX) _(_) _(CC,i) is P_(EMAX,i)−ΔT_(C), which represents thecapability of the duplex filter shall be better than the ΔT_(C)constraint, while the lower bound of P_(MAX) _(_) _(PA,j) isP_(POWERCLASS)−MPR_(PA,j)−A-MPR_(PA,j)−ΔT_(C,i), which represents thatbesides the duplex filter capability, the capability of the PA shall bebetter than the (MPR_(PA,j)+A-MPR_(PA,j)) constraint. Therefore, thelower bound of P_(MAX) _(_) _(PA,j) _(_) _(CC,i) should be decided bythe weaker one of the duplex filter capability and the PA capability. Asa result, it can be concluded that the lower bound of P_(MAX) _(_)_(PA,j,) _(_) _(CC,i) is min (P_(EMAX,i)−ΔT_(C),P_(POWERCLASS)−MPR_(PA,j)−A-MPR_(PA,j)−ΔT_(C,i)). The newly definedCC-level TPL P_(MAX PA,j) _(_) _(CC,i) replaces both (B7) and (B8) whenthe j-the PA only serves the i-th CC.

Once the different levels of TPLs have been determined and reduced tonon-redundant TPL values, the UE can calculate corresponding powerheadroom (PH) and perform PHR for each non-redundant TPL accordingly.There are two PHR schemes—complete PHR signaling and efficient PHRsignaling. In complete PHR signaling, one PHR for each non-redundant TPLis calculated by the UE and reported to the eNB, given that the eNBknows the UE/PA/CC mapping of the UE. In efficient PHR signaling, someof the layered TPL/PH information is combined or deduced to furtherreduce signaling overhead.

FIG. 5 is a flow chart of a method of complete power headroom reportingin accordance with one novel aspect. Suppose that a UE has a totalnumber of p PAs. In step 501, the UE starts with the j-th PA (j=1 . . .p, j++). In step 502, the UE checks whether the j-th PA serves only oneCC. If the answer is yes, then the PA-level TPL may be replaced by theCC-level TPL. The UE configures the CC-level TPL P_(MAX) _(_) _(CC,i)for the i-th CC served by the j-th PA based on equation (B12) (step503). The UE also reports the per-CC PHR based on equation (3) (step504). On the other hand, if there are more than one CCs served by thej-th PA, then the UE configures P_(MAX) _(_) _(CC,i) for the i-th CCserved by the j-th PA based on equation (4) (step 505). The UE alsoreports the per-CC PHR based on equation (3) (step 506). In step 507,the UE checks if there are more CCs in the j-th PA. If there is, thenthe UE repeats steps 505-506 until the TPL values for all the CCs servedby the j-th PA are configured. The UE then configures the PA-levelP_(MAX) _(_) _(PA,j) for the j-th PA based on equation (6), and reportsthe per-PA PHR based on equation (5) (step 508). In step 509, the UEchecks if there are more PAs. If the answer is yes, the UE goes back tostep 501 with an incremented j value and repeat step 502 through 508 foreach PA. If there is no more PAs, in step 510, the UE checks if the UEonly has one PA. If the answer is yes, then the complete PHR signalingis done because the UE-level TPL is replaced by the PA-level TPL basedon equation (A11). If the UE has more than one PA, then the UEconfigures UE-level P_(MAX) _(_) _(UE) based on equation (8), andreports per-UE PHR based on equation (7) (step 511).

FIGS. 6A and 6B are flow charts of a method of efficient power headroomreporting in accordance with one novel aspect. FIG. 6A illustrates afirst embodiment of efficient PHR signaling. In the first embodiment, aUE reports per-CC PHR for each CC plus per-UE PHR, while all PA-levelTPLs and UE-level TPL are combined into a new UE-level TPL. The per-CCPHR reporting is the same as illustrated in FIG. 5. In step 601, the UEstarts with the i-th CC (i=1 . . . n, i++). In step 602, the UEconfigures P_(MAX) _(_) _(CC,i) and reports per-CC PHR for the i-th CC.In step 603, the UE checks if there are more CCs. If there is, then theUE repeats steps 601-602 until all CCs have been completed for PHR. Instep 604, the UE configures a new UE-level TPL and reports per-UE PHR tothe eNB. The new UE-level TPL P_(MAX) _(_) _(UE)* is determined asfollows. Assume there are p PAs in the UE, i.e., PA1 to PAp. For PAj,(1<=j<=p), m(j) number of CCs are served, and the m(j) CCs are labeledas CCj(1), CCj(2), CCj(m). Then the corresponding PA-level TPL is givenasP _(CC,j(1)) + . . . +P _(CC,j(m(j))<=) P _(MAX) _(_)_(PA,j)(1<=j<=p)  (9)

Assume there are n active CCs in the UE, i.e., CC1 to CCn, and theUE-level TPL is P_(MAX) _(_) _(UE). As a result, the p PA-level TPLsdefined by equation (9) become redundant if the following new TPL isimposed:P _(CC,1) + . . . +P _(CC,n)<=min (P _(MAX) _(_) _(UE) ,P _(MAX) _(_)_(PA,1) , . . . ,P _(MAX) _(_) _(PA,p))Then, the new UE-level per-UE PHR is:P _(MAX) _(_) _(UE)*=min (P _(MAX) _(_) _(UE) ,P _(MAX) _(_) _(PA,1) , .. . ,P _(MAX) _(_) _(PA,p))PH_(UE) *=P _(MAX) _(_) _(UE) *−P _(UE)

FIG. 6B illustrates a second embodiment of efficient PHR signaling. Inthe second embodiment, a UE reports per-CC PHR for each CC, and the eNBknows the UE/PA/CC mapping. In this embodiment, if the eNB knows exactlythe values of CC-level TPL configured by the UE, then the eNB can obtainthe transmit power at each CC from per-CC PHR. In one example, the UEalways configures its CC-level TPL P_(MAX) _(_) _(CC,i) using the lowestallowable value, then the eNB knows the configured TPL values. Inanother example, the UE reports the configured TPL values to the eNBexplicitly. In the example of FIG. 6B, in step 611, the UE starts withthe i-th CC (i=1 . . . n, i++). In step 612, the UE configures P_(MAX)_(_) _(CC,i) and reports both the configured P_(MAX) _(_) _(CC,i) andper-CC PHR for the i-th CC to the eNB. In step 613, the UE checks ifthere are more CCs. If there is, then the UE repeats steps 611-612 untilall CCs have been completed for PHR. Since the UE/PA/CC mapping is knownto the eNB, the eNB knows all TPLs.

FIG. 7 illustrates a method of indicating UE transmit power capacity inaccordance with one novel aspect. In the example of FIG. 7, a UE isconfigured with two component carriers CC1 and CC2. The transmit powerover CC1 is P1 and the transmit power over CC2 is P2. The UE has thefollowing transmit power constraints: P1<=P_(CMAX,1) as denoted by avertical line 710, P2<=P_(CMAX,2) as denoted by a horizontal line 720,and P1+P2<=P_(CMAX) as denoted by a diagonal line 730. The transmitpower constraints P_(CMAX,1) and P_(CMAX,2) are the CC-level TPLsdefined above, while the transmit power constraint P_(CMAX) is theUE-level TPL defined above. A valid UE transmit power combination in thetwo CCs should fall in the intersection of the regions indicated by allthree power constraints, i.e., region #1 as denoted by the dotted-shade.On the other hand, if only one or two power constraints are used, thenthe UE transmit power may go outside region 1 into other regions such asregion #2, #3, or #4, as denoted by the slashed-shade.

To assist the network (eNB) in selecting a suitable resource allocationto a UE (e.g., the combination of MCS and the resource size/location)that does not result in the UE violating the power constraints, the UEis configured to provide regular PH information to the network. The UEtransmit power at CC and UE level can never exceed the limitations ofP_(CMAX,c) and P_(CMAX). If the calculated the transmit power are abovethe limits, the actual transmit power would be scaled down. That is, inFIG. 1, if the calculated transmit powers at CC and UE levels fall inregions #2, #3, or #4, or even in the outer area, the calculated powersare scaled down such that the actual transmit powers fall in region #1.In fact, power headroom is not a measure of the difference between themaximum transmit power and the actual transmit power. Rather, powerheadroom is a measure of the difference between the maximum transmitpower and the calculated transmit power (e.g., PHR₁=P_(CMAX,1)−P1, andPHR₂=P_(CMAX,2)−P2). Thus, a PH value can be negative, which indicatesthat the UE transmit power is already limited by the maximum transmitpower at the time of the PHR reporting.

Based on the illustration from FIG. 7, to enable the network to get afull picture of UE power usage, the UE should report the true values ofthe maximum transmit power along with PHRs, so that the network knowsthe exact boundaries of region #1. Generally, consider a UE that isconfigured with CC1, CC2, . . . , CCN. The power constraints areconfigured as:Pc<=P _(CMAX,C),1≦c≦N  (10)P1+P2+ . . . +PN≦P _(CMAX)  (11)

At each PHR reporting instance, the UE reports the following PHinformation to the network:

-   -   PHR₁, PHR₂, . . . , PHR_(N)    -   P_(CMAX,1), P_(CMAX,2), . . . , P_(CMAX,N); and    -   P_(CMAX)

A more general form of UE transmit power can be formulated if there aremore levels of transmit power limitations such as PA-level TPL asdescribed above. Suppose that there are K constraints for the transmitpower limitations, and they are referred to as constraints 1, 2, . . . ,K. Define a set Jk for 1<=k<=K, where the transmit power in the c-th CCis involved in the k-th constraint if c belongs to the set Jk. The powerlimitation for the k-th constraint is denoted by P_(MAX,K). Then,mathematically, we haveΣ_(c=1) ^(N) l _({cεJ) _(k}) *P _(c) ≦P _(MAX,k),1≦k≦K  (12)where l_({ }) is an indicator function equal to 1 if the condition inthe bracket { } is true, and equal to 0 otherwise. For example, thepower constraints in (10) and (11) can be embraced into (12) by settingK=N+1, J_(k)={k} for 1<=k<=N, J_(N+1)={1, 2, . . . , N},P_(MAX,k)=P_(CMAX,k) for 1<=k<=N, and P_(MAX,N+1)=P_(CMAX).

Consider a UE is configured with CC1, CC2, . . . , CCN, and the UEtransmit power limitation is governed by the equalities in (12).Considering this more generic setting, at each PHR reporting instance,the UE reports the following PH information to the network:

-   -   PHR₁, PHR₂, . . . , PHR_(N);    -   The value of K;    -   P_(MAX1), P_(MAX2), . . . , P_(MAXK); and    -   J₁, J₂, . . . , J_(K)

FIG. 8 is a flow chart of a method of indicating UE transmit powercapacity in accordance with one novel aspect. In step 801, a UEdetermines a total K number of transmit power limitation (TPL) values,the UE is configured with N number of component carriers (CCs). In step802, the UE reports power headroom (PH) information to an eNB. The powerheadroom information comprises N number of PH values for each CC, thevalue of K, the K number of TPL values, and K sets of carrierindexes—each set contains carrier indexes that are associated with acorresponding TPL.

Once a UE has configured all the necessary TPL values and calculated allthe power headroom to be reported, the PH information is signaled to itsserving eNB by radio resource control (RRC) layer messaging. Besides theexisting PHR triggers, new triggers for PHR may be defined. For example,when a new secondary cell (Scell) is added or removed, when resourceallocation or reference resource allocation changes, when the eNBrequests more power than the UE can support, i.e., the combined transmitpower is over the maximum power. Alternatively, the UE can autonomouslyactivate the PHR mechanism. When the PHR triggering condition issatisfied, the UE MAC layer prepares PH information and includes theinformation to a transmission block (TB). This TB is then sent over oneof the active CCs. For non-scheduled CC, a reference resource allocation(RRA) for calculating PHR is signaled by the eNB, or the UE can use apre-defined default RRA to calculate corresponding PH value.

FIG. 9 illustrates a power headroom reporting procedure between aneNB901 and a UE902 in an LTE/LTE-A wireless network in accordance withone novel aspect. In step 911, eNB901 transmits a PHR configurationmessage to UE902. In step 921, eNB91 optionally transmits referenceformat for the PHR configuration. Otherwise, default format may be used.In step 931, UE902 reports PHR #1 (e.g., per-PA PHR) to eNB901. In step941, UE902 reports PHR #2 (e.g., per-UE PHR) to eNB901. In step 951,UE902 reports PHR #3 (e.g., per-UE PHR and per-PA PHR) to eNB901.Finally, in step 961, UE902 reports PHR #4 (e.g., legacy PHR andper-UE/PA PHR) to eNB901.

To support PHR mechanism in wireless networks with carrier aggregation,new PHR format is needed. Either a fixed-length MAC control element (CE)or a variable-length MAC CE may be used for PHR. A mapping for a CC andits PH value needs to be indicated in the PHR. In one embodiment,implicit mapping may be used. For example, PH values have an ascendingor descending order according to its cell index. In another embodiment,explicit mapping may be used. For example, a bitmap or length indicatoris used in the PHR. Furthermore, the type of PHR needs to bedifferentiated by an indicator. The PHR contains a real PH value if thePH value is calculated using an actual transmission grant (# of PRB andmodulation order). On the other hand, a PHR contains a virtual PH valueif the PH value is calculated using a reference grant (# of PRB andmodulation order).

FIG. 10 illustrates examples of fixed-length MAC CE for PHR. In MACsub-header 1001, a new LCID is assigned for PHR. On per transmissiontime interval (TTI) basis, the length of the MAC CE is known to the eNB.For example, the length is a function of configured CCs, a function ofactivated CCs, or a function of scheduled CCs, all defined by the eNB inthe PHR configuration message. Within the MAC CE PDU, as illustrated inFIG. 10, the PH values are ordered from PH of PUCCH Pcell (also referredas type 2 PHR), PH of PUSCH PCell (also referred as type 1 PHR), andthen followed by PH values of PUSCH Scell, in ascending or descendingorder according to the cell index. A bit V indicates the type of PHR.

FIG. 11 illustrates examples of variable-length MAC CE for PHR. Similarto fixed length PHR, a new LCID is assigned in the MAC sub-header forvariable length MAC CE PHR. The length of the MAC CE is indicated eitherin the MAC sub-header or in the MAC CE PDU. As illustrated in the tophalf of FIG. 11, the length is indicated in the MAC sub-header 1101,which contains two octets, the first octet 1 contains the LCID, whilethe second octet 2 contains a bitmap used as the length indication. Forexample, a PH value of a CC is included in the MAC CE PDU only when acorresponding bit is set in the bitmap, so that the eNB can identify thelength of the MAC CE from the bitmap. In the bottom half of FIG. 11, thelength is indicated in the MAC CE PDU. Octet 1 in the MAC PDU contains abitmap used as the length indication.

FIG. 12 illustrates an embodiment of a new format for per-UE PHR. Toindicate that per-UE PHR is reported, one option is to use a new LCIDfor per-UE PHR. Another option is to use a bit 1201 inside the PHR PDUto indicate whether per-UE PHR is included, as illustrated in FIG. 12.The place to per-UE PHR may also have two options. A first option is toinclude the per-UE PHR right after the bitmap of the PHR MAC CE (e.g.,Place 1), while a second option is to include the per-UE PHR at the endof the PHR MAC CE (e.g., place 2). The reserved bit R may be used toindicate additional information of the per-UE PHR. Similar format may beused for per-PA PHR.

Although the present invention has been described in connection withcertain specific embodiments for instructional purposes, the presentinvention is not limited thereto. Accordingly, various modifications,adaptations, and combinations of various features of the describedembodiments can be practiced without departing from the scope of theinvention as set forth in the claims.

What is claimed is:
 1. A method, comprising: determining transmit powerlimitation (TPL) information by a UE in a wireless communication system,wherein the UE is configured with a plurality of component carriers(CCs) served by one or more power amplifiers (PAs), wherein the TPLinformation comprises a set of TPL values, each TPL value corresponds toa UE-configured maximum transmit power for the UE; determining powerheadroom (PH) information that comprises a set of PH values based on theTPL information; and reporting the PH information to a base station,wherein the TPL information is reduced to contain a reduced set ofnon-redundant TPL values, and wherein the PH information is also reducedto contain a reduced set of non-redundant PH values.
 2. The method ofclaim 1, wherein the set of TPL values comprises a UE-level TPL valuefor the UE, one or more PA-level TPL values for each PA, and a pluralityof CC-level TPL values for each CC.
 3. The method of claim 1, whereinthe set of PH values comprises a UE-level PH value for the UE, one ormore PA-level PH values for each PA, and a plurality of CC-level PHvalues for each CC.
 4. The method of claim 1, wherein the UE has onlyone PA, and wherein the UE-level TPL value for the UE is replaced by aPA-level TPL value for the PA.
 5. The method of claim 1, wherein a PAserves only one CC, and wherein a PA-level TPL value for the PA isreplaced by a CC-level TPL value for the CC.
 6. The method of claim 1,wherein the PH information is reported to the based station via afixed-length MAC control element (CE), wherein the length is configuredby the base station.
 7. The method of claim 1, wherein the PHinformation is reported to the based station via a variable-length MACcontrol element (CE), wherein the length is indicated in the MAC CE. 8.A user equipment (UE) device, comprising: a power control module thatdetermines transmit power limitation (TPL) information, wherein the UEis configured with a plurality of component carriers (CCs) served by oneor more power amplifiers (PAs), wherein the TPL information comprises aset of TPL values, each TPL value corresponds to a UE-configured maximumtransmit power for the UE, and wherein the power control moduledetermines power headroom (PH) information that comprises a set of PHvalues based on the TPL information; and a transmitter that reports thePH information to a base station, wherein the TPL information is reducedto contain a reduced set of non-redundant TPL values, and wherein the PHinformation is also reduced to contain a reduced set of non-redundant PHvalues.
 9. The device of claim 8, wherein the set of TPL valuescomprises a UE-level TPL value for the UE, one or more PA-level TPLvalues for each PA, and a plurality of CC-level TPL values for each CC.10. The device of claim 8, wherein the set of PH values comprises aUE-level PH value for the UE, one or more PA-level PH values for eachPA, and a plurality of CC-level PH values for each CC.
 11. The device ofclaim 8, wherein the UE has only one PA, and wherein the UE-level TPLvalue for the UE is replaced by a PA-level TPL value for the PA.
 12. Thedevice of claim 8, wherein a PA serves only one CC, and wherein aPA-level TPL value for the PA is replaced by a CC-level TPL value forthe CC.
 13. The device of claim 8, wherein the PH information isreported to the based station via a fixed-length MAC control element(CE), wherein the length is configured by the base station.
 14. Thedevice of claim 8, wherein the PH information is reported to the basedstation via a variable-length MAC control element (CE), wherein thelength is indicated in the MAC CE.
 15. A method, comprising: determininga total K number of transmit power limit (TPL) values for a userequipment (UE) in a wireless communication system, wherein the UE isconfigured with N number of component carriers (CCs); and reportingpower headroom (PH) information to a base station, wherein the PHinformation comprises N number of PH values for the N number of CCs andK number of TPL values, wherein the PH information is reported to thebased station via a MAC control element (CE), and wherein the length ofthe MAC CE for reporting the PH information is a function of a number ofCCs configured by the base station or indicated in the MAC CE.
 16. Themethod of claim 15, wherein the PH information further comprises thevalue of K.
 17. The method of claim 15, wherein one of the TPL valuesrepresents a UE-configured maximum transmit power for the UE.
 18. Themethod of claim 15, wherein the UE comprises a power amplifier (PA), andwherein one of the TPL values represents a UE-configured maximumtransmit power for the PA.
 19. The method of claim 15, furthercomprising: transmitting a maximum UE output power (P_(powerclass)) tothe base station.
 20. The method of claim 15, wherein the MAC CEsub-header contains a LCID assigned for PH information reporting.